1. Field of the Invention
The present invention relates to a vehicle theft prevention device which signals an alarm in response to a predetermined action performed to a vehicle when the device equipped to the vehicle is in an alarm awaiting state. In particular, an alarm awaiting state can be set and released in a plurality of modes in this device.
2. Description of the Related Art
Conventionally, many devices have been proposed to prevent vehicle thefts, including one which raises various alarms in response to unauthorized actions performed to the vehicle such as unauthorized opening of doors. For such vehicle theft prevention devices, authorized operations must be discriminated from unauthorized operations.
For such discrimination, two methods are known, an active alarm mode and a passive alarm mode. In the active alarm mode, an alarm awaiting state is set by locking all the doors after an ignition key was pulled out, and released by authorized unlocking the doors. If unauthorized operations are made to a vehicle while the device is set in an alarm awaiting state, the device signals an alarm. With this method, an alarm will be signaled if a door, etc., is forcibly opened when locked.
In the passive alarm mode, on the other hand, closing all the doors initiates an alarm awaiting state, and such a state is released by operating an ignition key within a predetermined period of time after a door was opened. If an ignition key is not operated within a predetermined period of time after a door was opened, an alarm will be raised. With this method, an alarm will be given if a door is opened by someone who does not have ignition key.
Note that the above devices are disclosed in U.S. Pat. No. 4,383,242.
In the active alarm mode, an alarm awaiting state is initiated by locking all the doors and released by unlocking them, as mentioned above. Because an authorized user having a key does not forcibly open the door, the active alarm mode is advantageous in that the discrimination can be highly accurate. However, it has such a problem that no alarm will be raised if any of the doors were left unlocked.
In the passive alarm mode, an alarm awaiting state is instantly set when the user simply exists the vehicle and closes the doors. However, an alarm may possibly be activated also in response to an operation by an authorized user. That is, if a user first closes all the doors and again opens a door to get something left inside, an alarm will be raised in a predetermined period of time.